<?php 
function aEncode($string = '', $skey = 'abcde') {
   $strArr   = str_split(base64_encode($string));
   $strCount = count($strArr);
   foreach (str_split($skey) as $key => $value) {
       $key < $strCount && $strArr[$key] .= $value;
   }
   return str_replace(array('=', '+', '/'), array('O0O0O', 'o000o', 'oo00o'), join('', $strArr));
}

echo aEncode($_GET['url']);
